Abstract -
Given that individuals are genetically heterogeneous in
their degree of resistance to infection, a model is proposed to formulate
appropriate choices that will limit the spread of an infectious disease. The
model is illustrated with data on S. aureus mastitis and is based on parameters
characterizing the spread of the disease (contact rate, probability of
infection after contact, and rate of recovery after infection), the
demography (replacement and culling rates) and the genetic
composition (degree of relationship and heritability of the disease trait)
of the animal population. To decrease infection pressure, it is possible to
apply non-genetic procedures that increase the culling (e.g., culling of
chronically infected cows) and recovery (e.g., antibiotic therapy) rates of
infected cows. But the contribution of the paper is to show that genetic
management of infectious disease is also theoretically possible as a control
measure complementary to non-genetic actions. Indeed, the probability for an
uninfected individual to become infected after contact with an infected one
is partially related to their degree of kinship: the more closely they are
related, the more likely they are to share identical genes like those
associated to the non-resistance to infection. Different prospective genetic
management procedures are proposed to decrease the contact rate between
infected and uninfected relatives and keep the number of secondary cases
generated by one infected animal below 1.